For the collection or detection (the terms being used interchangeably herein) of signals, and for the delivery of pulses for stimulation, such as for cardiac pacing, active implantable medical devices use electrodes that are incorporated into a lead that is connected to the generator of the device. The generator contains the signal collection circuits and the pulse generator circuits. The electrodes are intended to come into contact with the tissues from which an electrical signal is to be collected, and the tissues to be stimulated, such as the myocardium, nerve, or muscle tissues, as the case may be. In the case of a device for cardiac diagnosis and therapy, these electrodes can be endocardial (placed in a cavity of the myocardium in contact with the wall of the myocardium), epicardial (placed on an outside wall of the myocardium, in particular to define a reference potential, or to apply a shock) or intravascular (implanted, for example, in the coronary sinus artery to a location opposing the wall of the left ventricle).
A first aspect of the development of these active implantable devices is the increasing number of electrodes, particularly for those devices called “multisite” devices, that allow for choosing between different stimulation/detection sites and optimizing the operation of the device. The increasing number of electrodes can also result from the presence at a same level of the lead of several sector electrodes (which are electrodes specifically directed in a radial direction with respect to the lead, at the stimulation site), with the option to select one or another of these sector electrodes to optimize the delivery of pulses to the selected site. This is particularly true for leads implanted in the coronary venous system, for indirect stimulation of a left cavity: with several sector electrodes, it is relatively easy to choose the one that faces the wall of the epicardium in front of the cavity and in contact with the wall and thus to avoid phrenic nerve stimulation.
Another aspect of the development of implantable devices is the integration of different sensors into the lead, especially blood pressure or acceleration sensors, including endocardial acceleration (EA) sensors. The signals collected by these sensors provide information representative of the instantaneous hemodynamic status of the patient, allowing for more effective control of the various functions of the device.
These lead sensors also require a specific connection for the transmission of signals from the sensor, typically located at the distal end of the lead, to the generator connected at the opposite, proximal end. This connection is specific to the sensor and is superimposed on the specific connections existing between the generator and the various electrodes located in the distal region of the lead.
In any case, to accommodate as many conductors as there are electrodes would lead to both unacceptable dimensions for the lead and difficulties in manufacturing the lead, especially at the connecting link between the lead at its proximal end and the implantable generator to which it is coupled.
These developments, therefore, require the introduction of multiplexing electronic circuits to manage the exchange of multiple signals between the lead (electrodes and/or sensors) and the generator, and vice versa. Multiplexing is provided in situ, close to the electrodes by an electronic circuit (hereinafter simply called “chip”) embedded in the distal part of the lead, at or in the vicinity of its end (wherein the signals are collected and/or the pulses are to be delivered).
The EP 1938861 A1 (US counterpart: US2008/0177343) and EP 2082684 A1 (US counterpart: US2009/0192572) (all commonly owned by Sorin CRM S.A.S, previously known as ELA Medical, of Clamart France) describe such a lead having a plurality of electrodes, for example, ten electrodes, near its distal end associated with a chip, hermetically encapsulated in the vicinity of the electrodes in a rigid ring, providing the multiplexing/demultiplexing of the electrodes with a common bus formed by two insulated conductors extending along the entire length of the lead to the proximal connector, allowing the coupling with the generator, the latter being equipped with a counterpart demultiplexing/multiplexing circuit.
WO2010/091435 A2 and WO 2006/069322 A2 (Proteus Biomedical, Inc.) describe a system in which a common two-wire bus transmits signals from/to sector-addressable electrodes formed on “satellites” located on the lead at regular intervals. A multiplexing/demultiplexing chip is mounted inside the lead, and connected to the wires of the bus by means of welded micro-springs. The construction described, however, only leaves the lead with an internal lumen having a very small internal diameter relative to its outside diameter, due to the size of the chip and connections to the wires. This constraint limits the application of this technique to electrodes located at the distal end of lead, because the small lumen diameter would not allow the use of traditional techniques of implantation, unless by greatly increasing the outer diameter of the lead at the location of the those distal electrodes, which would in turn limit the applications. In addition, the implementation technology is extremely difficult to implement and its reliability over time has not been proven.